1. Field of the Invention
This invention relates generally to protective hearing devices and, more particularly, to protective hearing devices with active sound attenuation and control.
2. Background
Environmental sounds typically comprise a mixture of various sound wave frequencies having varying intensities. It is well documented that repeated or prolonged exposure to sound waves of certain frequencies and intensities can damage the auditory organ and cause serious hearing problems, including deafness. Injurious noises, such as those caused by explosions or bursts, are often comprised of a mixture of sound wave frequencies of varying intensity. These dangerous sound waves are in both the high and low frequency bands and have an intensity sufficient to cause hearing damage. Individuals who are frequently exposed to sound waves at dangerous frequencies and/or intensities run the risk of incurring permanent injuries, such as hearing loss or even deafness. Such individuals include workers at demolition or construction sites, operators of heavy, noisy equipment and those in active military service. These individuals need hearing protection to prevent losses in hearing acuity and/or gradual increases in hearing thresholds resulting from extended exposures to loud noises.
Passive sound attenuation devices which specifically address this problem are well known. These include conventional earplugs, earmuffs and the like, which function to reduce the negative effects of exposure to dangerous sound frequencies and intensities by limiting the entry of all sound waves into the auditory organ. These conventional devices suffer from a significant disadvantage, however; namely, that auditory access to environmental sounds of relatively risk free frequencies and intensities is also limited. In particular, these devices typically provide much greater attenuation at high frequencies than at low frequencies, as well as excessive attenuation at high frequencies. The result is that wearers of these devices who want or need to hear non-dangerous sounds are prevented from doing so. Therefore, while these devices may be protective against the effects of overexposure to sound having dangerous frequencies and intensities, they create a new danger in that they shut out all environmental sounds, including non-dangerous speech and warning sounds.
Active noise cancellation has been another approach to noise reduction. Active noise cancellation systems eliminate unwanted sound using destructive interference. Cancellation is achieved by propagating xe2x80x9canti-noise,xe2x80x9d identical to the unwanted sound waves, but inverted. The anti-noise waves interact with the unwanted noise wave resulting in cancellation. A feedback active cancellation headset typically includes a sound generator in each earpiece for producing anti-noise, and a residual microphone, also located in each earpiece, to provide feedback signals to a controller that generates the anti-noise signals. Each microphone detects the unwanted noise within each earpiece and provides corresponding signals to the controller. The controller supplies anti-noise signals to the sound generator corresponding to the noise detected in the earpieces, but inverted, with respect to the unwanted waveform. When the anti-noise interacts with the noise within each earpiece, destructive interference between the noise and the anti-noise cancels the unwanted sound.
For example, U.S. Pat. No. 5,600,729 to Darlington et al. discloses a device comprising a microphone located upstream of a loudspeaker relative to the approaching direction of unwanted noise waves, in an assembly adapted to be mounted at a site of entry of the noise into the ear chamber. The output of the microphone is amplified and fed to the downstream loudspeaker to produce noise that tends to cancel the unwanted intrusive noise. The device is attached by means of a headband.
U.S. Pat. No. 3,890,474 to Glicksberg discusses the incorporation of sound amplitude limiting into a device that is self-contained in the ear canal of the wearer. The sound amplitude limiter is designed so that most un-transduced sound is blocked out from reaching the middle ear by a highly effective sound absorbing material which is located within the ear piece. The earpiece has a thin-walled outer casing sized to provide an airtight fit inside the ear canal. Proper fit is achieved either by custom shaping each device for a particular wearer, or by providing an array of various shaped devices for a wearer to choose from.
U.S. Pat. No. 5,355,418 to Kelsey et al. discusses a frequency selective hearing protection device. When worn in the manner shown, this device performs a natural sound blocking function. It utilizes adaptive filtering to hinder the transmission of frequency components in ambient sound above a predetermined threshold. The device is encompassed in an ear unit fitting in the concha (outer ear) and having a plug portion partially inserted into the ear canal. The device must be appropriately sized for each wearer.
U.S. Pat. No. 5,305,387 to Sapiejewski discusses an earphone for use in an active noise reduction system. This earphone includes a shell accommodating a microphone closely adjacent to a driver shaped and sized to fit in the concha of an ear. A cushion is made of silicon gel covered by polyurethane film and is custom shaped for each wearer to provide comfort and a seal without moving the microphone away from the ear canal.
Embodiments are described in certain of the above references that employ earmuffs. However, the bulky size of earmuffs renders them inappropriate for many applications. For instance, earmuffs must seal the entire ear. Thick or long hairstyles can compromise the seal. Earmuffs can also interfere with the use of safety glasses or prescription glasses, protective gear, shields, gas masks, helmets, and cold weather clothing. Therefore, active noise reduction systems that mount within the wearer""s ear are often preferable to earmuffs. However, inserting an audio device inside the ear canal raises safety and comfort issues analogous to those addressed by hearing aid designers. In that regard U.S. patent application Ser. No. 09/161,344, which is fully incorporated herein by reference, discloses a hearing device having a soft conformal tip that can be securely seated within the deep bony region of the ear canal, without causing appreciable pain or discomfort to the wearer.
Though active noise reduction systems mounted in the ear canal typically perform better than, for instance, systems mounted in earmuffs, a disadvantage of mounting such systems within the wearers ear is that conventional devices must each be custom fit to the individual wearer, increasing system cost.
For instance, U.S. Pat. No. 5,740,258 to Goodwin-Johansson discusses an active noise suppressor that fits in an ear canal without blocking the ear canal. The acoustically unobstructed passage allows the active reduction of undesired noise portions, while allowing the desired portions of the sound pressure waves to reach the eardrum. An integral housing is disclosed for securing the device inside the ear canal. The housing consists of elastic ribs attached to the circuit board, the ribs lodging the device in the ear canal.
U.S. Pat. No. 4,985,925 to Langberg et al. discloses an electronic earplug seated in the concha fossa (outer ear), which combines active and passive noise reduction in the quiet zone at the ear. The electronic earplug maintains an acoustical seal with a concha fossa and/or the external auditory meatus (ear canal). Noise that penetrates this passive barrier and reaches the quiet zone formed around the occluded ear canal volume adjacent the eardrum is further reduced by active means. However, neither Langberg et al. or Goodwin-Johansson address the problems of using xe2x80x9cuniversal fitxe2x80x9d devices for an in-the-ear-canal, active noise reduction system.
In particular, existing active noise reduction technology has several disadvantages. For instance, all the active noise reduction systems described above employ xe2x80x9cfeedback cancellationxe2x80x9d systems to cancel unwanted noise. A problem associated with feedback cancellation systems is that they are prone to instability. Feedback systems tend to become unstable, for example, if the bandwidth of the system is too broad or the gain of the system is too high. When instability occurs, the system usually emits a loud noise that is generally unpleasant and occasionally dangerous. Consequently, the maximum range and effectiveness of feedback systems are limited by parameters designed to keep the feedback system stable.
To effect maximum cancellation, the waveform of the interacting anti-noise should exactly match the unwanted waveform, but should be inverted. The acoustic properties of each device, however, affect the characteristics of the anti-noise waveform. The effect of the acoustic properties may be corrected by processing the residual signal according to a transfer function characteristic of the acoustic properties of the system to compensate for the effects. However, these acoustic properties of the device are not constant under all conditions, and may vary with the force applied to the device in the wearer""s ear. For example, when high pressure is applied to the device, or when the device is removed from the wearer""s ear, the variation of the device""s acoustic properties, particularly the volume and acoustic resistance, may cause instability in the feedback loop. This instability, in turn, causes the control loop to generate unstable oscillations, producing unpleasant and potentially even harmful noise.
In addition, many noise cancellation systems are designed not only to cancel unwanted noise, but also to provide particular sounds to the wearer. For example, earmuffs for listening to music or for use by pilots ideally cancel extraneous noise, and transmit particular desired sounds to the listener. Conventionally, the desired input signal is mixed with the residual signal from the internal microphone so that the desired signal is not canceled by the system. Feedback noise cancellation systems, however, because of their limited bandwidth, exhibit a high frequency rolloff having a relatively low cutoff frequency. Because of this cutoff frequency, higher frequencies of the desired sound tend to be attenuated, degrading the quality of the signal. Consequently, an equalizer must be added to return the sound to its proper amplitude.
In summary, noise-attenuating systems employing feedback noise cancellation have many disadvantages, including sensitivity to component location and unstability. Therefore, there is a need not only for an effective, low-cost, universal, in-the-ear-canal, active noise reduction system, but also for an active noise reduction system that does not exhibit the problems associated with feedback noise cancellation systems.
These needs and others are addressed by the noise attenuating devices and systems of the present invention. In a preferred embodiment, an earplug is provided having a replaceable soft tip, electronics with integrated multi-band automatic amplitude control, and active noise attenuation without feedback noise cancellation. The earplug preferably fits at least partially in the ear canal, and does not interfere with glasses, long hair, helmets, or cold weather clothing, etc. The earplug passively blocks sound waves having dangerous amplitudes and actively monitors incoming sound waves using a multi-channel automatic volume control circuit, passing through non-dangerous sound waves, and allowing the wearer to communicate in noisy environments. The earplug preferably avoids the cost of custom-fit devices by providing a universal earplug core comprising electronics along with a low-cost, disposable, universal soft tip to interface between the wearer""s ear canal and the earplug core.
According to one aspect of the invention, a noise attenuating system in the earplug includes a core portion, comprising electronics and a housing. The electronics are adapted to attenuate unsafe amplitude sounds, and may comprise a microphone, circuitry, a speaker, and a battery. The circuitry receives a signal from the microphone, filters the signal into a plurality of bands, identifies each of the bands as corresponding either to a safe or unsafe amplitude sound, attenuates the unsafe amplitude sounds, and outputs to the speaker signals corresponding to safe amplitude sounds. The electronics thus actively filter sound, but do not provide active feedback cancellation. Instead of using feedback to cancel a sound wave, the system initially blocks all sound waves passively, then actively filters the sound waves, passing through sound waves of safe amplitude, such as speech sounds.
According to another aspect of the invention, the noise attenuating system further includes a deformable member, such as a disposable soft tip, adapted to fit at least partially inside a wearer""s ear canal. In one embodiment, a universal deformable member has a hollow portion adapted to receive the core portion. The universal core portion can be inserted into the universal deformable member, and the assembly can be inserted at least partially into the ear canal. The core portion becomes removably engaged with the deformable member upon assembly. The deformable member holding the core portion deforms to the contour of the wearer""s ear canal upon insertion, allowing the use of a universal core portion in a variety of differently shaped ear canals.
According to a further aspect of the invention, the electronics can comprise on/off switches, or switches facilitating the programming of the circuitry for different uses, such as switches for adjusting signal attenuation, frequency selection, and magnitude of noise suppression.
According to yet another aspect of the invention, the circuitry can be adapted to actively attenuate sound signals according to an active noise suppression algorithm. According to a still further aspect of the invention, an elongated flexible member is provided, such as a cord, which can be adapted to connect two earplugs. In one embodiment the elongated flexible member connects the core portions, while in another embodiment the elongated flexible member connects the deformable members. In yet other embodiments, the elongated flexible member connects either a core portion or a deformable member with another deformable member, such as a conventional earplug.
According to still another aspect of the invention, the elongated flexible member can comprise any or all of the electronics. For instance, the microphone can be attached to the elongated flexible member, and can be in communication with either one or two earplugs connected with the elongated flexible member. Likewise, all of the electronics can be attached with the elongated flexible member, as long as the sound waves output by the speaker are in communication with the interior of at least one ear canal.
Yet another aspect of the invention comprises adapting the noise attenuating electronics to earmuffs. Embodiments are provided for applications where earmuffs may be preferable to in-the-ear-canal devices, such as where the wearer already wears a hearing aid. Adding the active noise-filtering electronics of the present invention to otherwise conventional earmuffs allows wearers to hear safe amplitude sounds, which are broadcast by a speaker in the region between the earmuff and the ear, while avoiding unsafe amplitude sounds, which the earmuffs block through passive noise attenuation, and the electronics further attenuate. Another embodiment utilizes the same electronics module as the earplugs, such that the electronics module, or core portion, would be interchangeable between the earmuffs and the earplugs.
An additional aspect of the invention comprises adapting the noise attenuating electronics to a behind-the-ear device. In this embodiment, the noise attenuating electronics, other than the speaker, are located in a behind-the-ear housing similar to a behind-the-ear hearing aid device. The attenuated signal is sent via an electrical wire or other communication channel from the behind-the-ear device to a speaker mounted in a deformable member inside the ear canal. Embodiments positioning the housing in locations other than behind the ear are also contemplated in this aspect of the invention.
Other and further aspects and advantages of the invention will become apparent hereinafter.